In agriculture, wide use is made of distribution devices mounted on booms for various uses. Spraying booms are in particular used for various pesticide or phytopharmaceutical products. Use may also be made of booms for distributing liquids without spraying them; thus, it is possible to distribute liquid fertilizers, particularly fertilisers in solution form, with the aid of booms. Booms may in addition be used for distributing solid materials, such as seeds, and in particular pulverulent materials, such as solid fertilizers.
These distribution booms are mounted on towed or self-propelled vehicles, which have to move over fields whose surface is irregular and which may also contain slopes or may themselves be hillsides. As the result of the irregularities of the ground in relation to the wheels of the vehicles moving thereon (clods, stones, tyre marks, furrows, etc.), there is generally a disordered movement of the free ends of the boom, which is fixed to the carrier vehicle only at its centre. This movement, the amplitude of which may be very considerable in the case of long booms, is the cause of considerable irregularities in the distribution of the materials.
It should be noted that this irregular movement may be split up into a whipping movement in a horizontal plane and a rolling movement in the vertical plane perpendicular to the direction of advance. In addition to its effect on the irregularity of distribution of the materials, the rolling may be so considerable that the boom touches the ground, so that it may be damaged.
Various devices are known for reducing the rolling effect of the booms, mentioned above, and attention in particular is drawn to French Pat. No. 1,564,543 (Evrard), Belgian Pat. No. 795,007 (De Meeus), U.S. Pat. No. 3,680,505 (Loeffler), and German Patent Application DT-OS No. 2,160,227 (Maass).
Devices disclosed by the prior art mentioned above essentially propose to suspend the boom with the aid of two connecting rods. However, these disclosures are only partly successful, in the sense that in the case of considerable irregularity of the ground, the rolling of the boom is not completely limited, and in particular, a boom of long span may actually touch the ground under the jotting action. Furthermore, the prior art is effective only for substantially horizontal ground, that is to say, ground where, with the exception of localised irregularities of the surface, the axle of the vehicle carrying the boom moves in a substantially horizontal plane. If the machine is intended for hillside working, no simple mechanical solution has been proposed for keeping the boom parallel to the slope of the ground. Hydraulic control is of course possible, but is expensive and difficult to operate. The longer the boom, the greater these difficulties will become.